The invention relates to a method and apparatus for determining the proportions of the air-fuel mixture constituents supplied to an internal combustion engine by a mixture preparing device. The apparatus has at least two .lambda. or oxygen sensors arranged in the exhaust gas conduit system of the engine. The output signals of the oxygen sensors are integrated and supplementarily used in the determination of the air-fuel mixture proportions.
Of special concern is an internal combustion engine which utilizes a fuel injection device as the mixture preparing device, which precalculates the quantity of fuel to be delivered by using the rpm and the air flow rate delivered to the internal combustion engine.
Mixture preparing devices are already known, which operate with a single .lambda. sensor in the exhaust gas conduit system. In such devices, the .lambda. sensor output signal is evaluated in such a manner that it is supplementarily used, after processing by a subsequently arranged integrator, to precisely determine the proportions of the constituents of the air-fuel mixture supplied to an internal combustion engine. The output signal of the .lambda. sensor whereby forms the actual value signal of a regulating system, which includes the internal combustion engine itself as the regulated system.
It has also been suggested, for mixture preparing devices used with the more complicated engines, to operate with at least two .lambda. sensors arranged at suitable locations in the engines or the exhaust gas conduit systems thereof; or to arrange at least two .lambda. sensors at various locations in an exhaust gas conduit system for a more comprehensive determination of the exhaust gas composition. The evaluation of the output signals of the two .lambda. sensors can thereby take place with the aid of a single integrator circuit, whereby the sensor signals are alternately switched in a cyclical manner to the input of the integrator circuit. The single integrator circuit then delivers its output signal for the mixture composition to the mixture preparing device. In this manner, however, one does not exhaust the many possibilities that are offered by the use of two .lambda. sensors in a control situation, and in particular, with such an arrangement the dynamic behavior of the mixture preparation cannot be improved.
The use of two separate units for a certain number of cylinders in larger internal combustion engines, for example, for half of the cylinders, has also been suggested. Thus in V-engines a separate mixture preparing device is provided for each row of cylinders. This solution, however, is very expensive, and cannot optimally employ the special characteristics that the use of two .lambda. sensors makes available.